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Abstract:

There are provided a wireless communicator that performs channel
scanning, in a period during which wireless communication is not
performed, to detect a frequency channel currently used by a surrounding
wireless communication device; a frequency channel information storage
that stores frequency channel information indicating the frequency
channel detected by the wireless communicator; and a travel information
acquisition unit that acquires travel information indicating motion of a
vehicle. A switch controller performs switching control of a frequency
channel used by the wireless communicator in accordance with the
frequency channel information and the travel information acquired by the
travel information acquisition unit.

Claims:

1: A wireless communication device that is installed in a moving object
and that selects an arbitrary frequency channel from among a plurality of
frequency channels and performs wireless communication by using the
selected frequency channel, the wireless communication device comprising:
a wireless communicator that performs wireless communication with another
wireless communication device using the frequency channel, while
performing channel scanning to detect a frequency channel currently used
by a surrounding wireless communication device, the channel scanning
being performed in a period during which the wireless communication is
not performed; a frequency channel information storage that stores
frequency channel information indicating the frequency channel detected
by the wireless communicator; a travel information acquisition unit that
acquires travel information indicating motion of the moving object in
which the wireless communication device is installed; and a switch
controller that performs switching control of the frequency channel used
by the wireless communicator in accordance with to the frequency channel
information stored in the frequency channel information storage and the
travel information acquired by the travel information acquisition unit.

2: The wireless communication device according to claim 1, wherein, when
a travel speed of the moving object as the travel information is acquired
by the travel information acquisition unit, the switch controller does
not perform the switching control of the frequency channel used by the
wireless communicator in a case where the acquired travel speed is equal
to or more than a predetermined speed threshold, while performing said
switching control only in a case where the acquired travel speed is less
than the predetermined speed threshold.

3: The wireless communication device according to claim 1, wherein the
frequency channel information storage records a number of detection of
the frequency channel performed by the wireless communicator when storing
the frequency channel information indicating the frequency channel
detected by the wireless communicator, and in a case where the switch
controller changes the frequency channel used by the wireless
communicator when a travel speed of the moving object as the travel
information is acquired by the travel information acquisition unit, the
switch controller sets a higher interference detection threshold for a
higher travel speed of the moving object acquired by the travel
information acquisition unit, excludes, from selection, a frequency
channel whose number of detection recorded in the frequency channel
information storage exceeds the interference detection threshold, and
selects a frequency channel to be used by the wireless communicator from
among frequency channels other than the excluded frequency channel.

4: A wireless communication device that is installed in a moving object
and that selects an arbitrary frequency channel from among a plurality of
frequency channels and performs wireless communication using the selected
frequency channel, the wireless communication device comprising: a
wireless communicator that performs wireless communication with another
wireless communication device using the frequency channel, while
performing channel scanning to detect a frequency channel currently used
by a surrounding wireless communication device, the channel scanning
being performed when a channel detection request is received; a frequency
channel information storage that stores frequency channel information
indicating the frequency channel detected by the wireless communicator; a
travel information acquisition unit that acquires travel information
indicating motion of the moving object in which the wireless
communication device is installed; and a switch controller that outputs
the channel detection request to the wireless communicator depending on
the travel information acquired by the travel information acquisition
unit, and performs switching control of the frequency channel used by the
wireless communicator in accordance with the frequency channel
information stored in the frequency channel information storage.

5: The wireless communication device according to claim 4, wherein the
switch controller determines whether surrounding condition of the moving
object has changed by using the travel information acquired by the travel
information acquisition unit, and when the switch controller determines
that the surrounding condition has changed, outputs a channel detection
request to the wireless communicator and performs the switching control
of the frequency channel used by the wireless communicator in accordance
with the frequency channel information stored in the frequency channel
information storage.

6: A wireless communication device that is installed in a moving object
and that selects an arbitrary frequency channel from among a plurality of
frequency channels and performs wireless communication by using the
selected frequency channel, the wireless communication device comprising:
a wireless communicator that performs wireless communication with another
wireless communication device using the frequency channel, while
performing channel scanning to detect a frequency channel of a channel
number included in a channel detection list, the channel scanning being
performed in a period during which the wireless communication is not
performed; a frequency channel information storage that stores frequency
channel information indicating the frequency channel detected by the
wireless communicator; a travel information acquisition unit that
acquires travel information indicating motion of the moving object in
which the wireless communication device is installed; and a switch
controller that outputs, to the wireless communicator, a channel
detection list including a channel number of a frequency channel as a
detection target depending on the travel information acquired by the
travel information acquisition unit, and performs switching control of
the frequency channel used by the wireless communicator in accordance
with the frequency channel information stored in the frequency channel
information storage.

7: The wireless communication device according to claim 6, wherein, when
a travel speed of the moving object as the travel information is acquired
by the travel information acquisition unit, the switch controller reduces
quantity of the channel number to be included in the channel detection
list as the travel speed indicates higher value.

8: The wireless communication device according to claim 1, further
comprising a switching time information storage that stores switching
time information indicating a switching time at which the switching
control of the frequency channel is performed by the switch controller,
wherein the switch controller performs switching control of the frequency
channel used by the wireless communicator in accordance with the
frequency channel information stored in the frequency channel information
storage, the travel information acquired by the travel information
acquisition unit, and the switching time information stored in the
switching time information storage.

9: The wireless communication device according to claim 8, wherein, when
a travel speed of the moving object as the travel information is acquired
by the travel information acquisition unit, the switch controller does
not perform the switching control of the frequency channel used by the
wireless communicator in a case where the acquired travel speed is equal
to or more than a predetermined speed threshold, calculates elapsed time
from when the frequency channel is last switched by referring to the
switching time information stored in the switching time information
storage in a case where the acquired travel speed is less than the
predetermined speed threshold, and does not perform the switching control
of the frequency channel used by the wireless communicator in a case
where the elapsed time is less than a predetermined elapsed time
threshold, while performing said switching control in a case where the
elapsed time is equal to or more than the predetermined elapsed time
threshold.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a wireless communication device
that selects an arbitrary frequency channel from among a plurality of
frequency channels and performs wireless communication with another
wireless communication device installed in another vehicle by using the
frequency channel.

BACKGROUND ART

[0002] When wireless communication is performed between a plurality of
wireless communication devices installed in different vehicles, in order
to avoid the occurrence of interference with other wireless
communications, switching control of frequency channel is performed. In
the switching control, channel scanning is performed to detect frequency
channels currently used by surrounding wireless communication devices,
and a frequency channel used for wireless communication is changed to an
unused channel.

[0003] A method of appropriately changing a frequency channel in wireless
communication in a vehicle according to communication conditions is
disclosed in, for example, the following Patent Document 1.

[0004] In the disclosed method, quality of image data is measured as a
characteristic of a currently used frequency channel, and the measurement
period is changed according to the moving speed of a vehicle.
Specifically, the change is made such that the longer measurement period
is set as the moving speed of the vehicle is getting higher.

[0005] By changing the measurement period according to the moving speed of
the vehicle, measurement accuracy can be improved. It enables the
wireless communication to perform frequency channel switching depending
on communication conditions.

CITATION LIST

[0006] Patent Literature 1: JP 2010-068351 A (Paragraph

[0037] and FIG. 7)

SUMMARY OF INVENTION

[0007] Since the conventional wireless communication device is configured
in the above-described manner, by changing the measurement period of the
quality of image data according to the moving speed of the vehicle, the
frequency channel is appropriately changed. However, since the frequency
channel is changed when the quality of image data has deteriorated,
communication conditions have already deteriorated at the time of
changing the frequency channel. Therefore, there is a problem that the
influence on communication is great.

[0008] In addition, although the measurement period of the quality of
image data is changed according to the moving speed of the vehicle, the
timing at which the frequency channel is changed is unrelated to the
moving speed of the vehicle. Therefore, there is a problem that the
frequency channel is frequently changed even in the state where the
wireless communication is influenced by interference in a short time
(i.e. the state where the vehicle is traveling at high speed).

[0009] The invention is made to solve problems such as those described
above, and an object of the present invention is to provide a wireless
communication device which is capable of suppressing the excessive
channel switching without causing an increase in the influence of
interference on wireless communication.

[0010] A wireless communication device according to the present invention
includes: a wireless communicator that performs wireless communication
with another wireless communication device using a frequency channel,
while performing channel scanning to detect a frequency channel currently
used by a surrounding wireless communication device, the channel scanning
being performed in a period during which the wireless communication is
not performed; a frequency channel information storage that stores
frequency channel information indicating the frequency channel detected
by the wireless communicator; a travel information acquisition unit that
acquires travel information indicating motion of a vehicle in which the
wireless communication device is installed; and a switch controller that
performs switching control of the frequency channel used by the wireless
communicator in accordance with to the frequency channel information
stored in the frequency channel information storage and the travel
information acquired by the travel information acquisition unit.

[0011] According to the invention, the configuration is such that there
are provided: a wireless communicator that performs wireless
communication with another wireless communication device using a
frequency channel, while performing channel scanning to detect a
frequency channel currently used by a surrounding wireless communication
device, the channel scanning being performed in a period during which the
wireless communication is not performed; a frequency channel information
storage that stores frequency channel information indicating the
frequency channel detected by the wireless communicator; a travel
information acquisition unit that acquires travel information indicating
motion of a vehicle in which the wireless communication device is
installed; and a switch controller that performs switching control of the
frequency channel used by the wireless communicator in accordance with to
the frequency channel information stored in the frequency channel
information storage and the travel information acquired by the travel
information acquisition unit. Therefore, there is an effect of being able
to suppress excessive channel switching without causing an increase in
the influence of interference on wireless communication.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a configuration diagram showing a wireless communication
device according to Embodiment 1 of the present invention.

[0013]FIG. 2 is a flowchart showing the processing content of a switch
controller 4 of the wireless communication device according to Embodiment
1 of the present invention.

[0014]FIG. 3 is a configuration diagram showing a wireless communication
device according to Embodiment 2 of the present invention.

[0015]FIG. 4 is a flowchart showing the processing content of a switch
controller 6 of the wireless communication device according to Embodiment
2 of the present invention.

[0016]FIG. 5 is a configuration diagram showing a wireless communication
device according to Embodiment 3 of the present invention.

[0017]FIG. 6 is a flowchart showing the processing content of a switch
controller 9 of the wireless communication device according to Embodiment
3 of the present invention.

[0018] FIG. 7 is a configuration diagram showing a wireless communication
device according to Embodiment 4 of the present invention.

[0019]FIG. 8 is a flowchart showing the processing content of a switch
controller 11 of the wireless communication device according to
Embodiment 4 of the present invention.

[0020]FIG. 9 is a configuration diagram showing a wireless communication
device according to Embodiment 5 of the present invention.

[0021] FIG. 10 is a flowchart showing the processing content of a switch
controller 13 of the wireless communication device according to
Embodiment 5 of the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiment 1

[0022] FIG. 1 is a configuration diagram showing a wireless communication
device according to Embodiment 1 of the present invention.

[0023] The wireless communication device of FIG. 1 is a device that is
installed in a vehicle and that selects an arbitrary frequency channel
from among a plurality of frequency channels and performs wireless
communication with another wireless communication device installed in
another vehicle by using the frequency channel.

[0024] In FIG. 1, a wireless communicator 1 is composed of, for example, a
communication device in which a modulator, a demodulator, etc. are
mounted. The wireless communicator 1 performs the process of performing
wireless communication with another wireless communication device by
using a frequency channel given by a switch controller 4. The wireless
communicator 1 performs channel scanning in a period during which the
wireless communication is not performed. The channel scanning is
performed to detect frequency channels currently used by surrounding
wireless communication devices.

[0025] A frequency channel information storage 2 is composed of, for
example, a storage device such as a RAM or a hard disk, and stores
frequency channel information indicating the frequency channels detected
by the wireless communicator 1.

[0026] Note that the frequency channel information includes not only
information indicating the frequency channels detected by the wireless
communicator 1, but also information indicating the received signal
strengths of the frequency channels.

[0027] A travel information acquisition unit 3 is composed of, for
example, a semiconductor integrated circuit on which a CPU is mounted, a
one-chip microcomputer, or the like. The travel information acquisition
unit 3 performs the process of acquiring a vehicle travel speed, etc., as
travel information indicating the motion of the vehicle in which the
wireless communication device is installed.

[0028] The switch controller 4 is composed of, for example, a
semiconductor integrated circuit on which a CPU is mounted, a one-chip
microcomputer, or the like. The switch controller 4 performs switching
control of the frequency channel used by the wireless communicator 1 in
accordance with the frequency channel information stored in the frequency
channel information storage 2 and the travel information acquired by the
travel information acquisition unit 3.

[0029] Specifically, when a vehicle travel speed V acquired by the travel
information acquisition unit 3 is equal to or more than a predetermined
speed threshold Vth, the switch controller 4 does not perform the
switching control of the frequency channel used by the wireless
communicator 1. On the other hand, when the travel speed V is less than
the speed threshold Vth, the switch controller 4 performs the
switching control to select a frequency channel to be used by the
wireless communicator 1 and gives the selected frequency channel to the
wireless communicator 1.

[0030] In the example represented by FIG. 1, it is assumed that the
wireless communicator 1, the frequency channel information storage 2, the
travel information acquisition unit 3, and the switch controller 4, which
are the components of the wireless communication device is composed of
dedicated hardware. Alternatively, a part of those components or the
whole ones may be composed of a computer.

[0031] When the entire wireless communication device is composed of a
computer, a program in which the processing content of the wireless
communicator 1, the frequency channel information storage 2, the travel
information acquisition unit 3, and the switch controller 4 is written
may be stored in a memory of the computer, and thus a CPU of the computer
may implement the stored program in the memory.

[0032] In addition, when a part of the wireless communication device
(e.g., the switch controller 4) is composed of a computer, a program in
which the process content of the switch controller 4 is written may be
stored in a memory of the computer, and a CPU of the computer may
implement the stored program in the memory.

[0033]FIG. 2 is a flowchart showing the processing content of the switch
controller 4 of the wireless communication device according to Embodiment
1 of the present invention.

[0034] The operation will be described.

[0035] The wireless communicator 1 performs wireless communication with
another wireless communication device by using a frequency channel given
by the switch controller 4 which will be described later.

[0036] In addition, the wireless communicator 1 performs channel scanning
in a period during which the wireless communication is not performed in
order to detect frequency channels currently used by surrounding wireless
communication devices.

[0037] On detecting a frequency channel currently used by a surrounding
wireless communication device, the wireless communicator 1 measures a
received signal strength S of the detected frequency channel. The
wireless communicator 1 outputs frequency channel information including
information on the frequency channel and the received signal strengths S
to the frequency channel information storage 2.

[0039] The travel information acquisition unit 3 acquires, for example, a
vehicle travel speed V as travel information indicating motion of the
vehicle from a speedometer of the vehicle in which the wireless
communication device is installed.

[0041] After acquiring the frequency channel information, the switch
controller 4 recognizes the frequency channels currently used by the
surrounding wireless communication devices by referring to the frequency
channel information, and determines whether the frequency channels
include the same channel as or an adjacent channel to the frequency
channel currently used by the wireless communicator 1 (step ST2).

[0042] If the frequency channels currently used by the surrounding
wireless communication devices do not include the same or adjacent
channel as/to the frequency channel currently used by the wireless
communicator 1, the switch controller 4 does not change the frequency
channel currently used by the wireless communicator 1 because the
communication is not influenced by interference (step ST3).

[0043] On the other hand, if the frequency channels currently used by the
surrounding wireless communication devices include the same or adjacent
channel as/to the frequency channel currently used by the wireless
communicator 1, the switch controller 4 recognizes the received signal
strengths S of the frequency channels currently used by the surrounding
wireless communication devices by referring to the frequency channel
information because the communication may be influenced by interference.
Then the switch controller 4 determines whether the received signal
strengths S of the frequency channels are equal to or more than a
predetermined strength threshold Sth (step ST4).

[0044] If the received signal strengths S of the frequency channels
currently used by the surrounding wireless communication devices are less
than the strength threshold Sth, the switch controller 4 does not
change the frequency channel currently used by the wireless communicator
1 (step ST3). This is because it is less likely that the communication is
influenced by interference (even if the communication is influenced by
interference, the influence is considered to be small).

[0045] On the other hand, if the received signal strengths S of the
frequency channels currently used by the surrounding wireless
communication devices are equal to or more than the strength threshold
Sth, the switch controller 4 acquires the vehicle travel speed V
from the travel information acquisition unit 3 (step ST5). This is
because it is highly likely that the communication is influenced by
interference.

[0046] After acquiring the vehicle travel speed V from the travel
information acquisition unit 3, the switch controller 4 determines
whether the vehicle travel speed V is equal to or more than a
predetermined speed threshold Vth (step ST6).

[0047] If the vehicle travel speed V is equal to or more than the
predetermined speed threshold Vth, the switch controller 4 does not
change the frequency channel currently used by the wireless communicator
1 (step ST3). This is because it is considered that the time required for
the vehicle to get away from a location where the communication is
interfered is short, and thus the period of time during which the
communication is influenced by the interference is short.

[0048] On the other hand, if the vehicle travel speed V is less than the
predetermined speed threshold Vth, the switch controller 4 changes
the frequency channel currently used by the wireless communicator 1. This
is because it is considered that the time required for the vehicle to get
away from a location where the communication is interfered is long and
thus the period of time during which the communication is influenced by
the interference is long.

[0049] Specifically, the switch controller 4 selects any one frequency
channel from among usable frequency channels other than the frequency
channels included in the frequency channel information stored in the
frequency channel information storage 2 (step ST7).

[0050] When the switch controller 4 changes the frequency channel
currently used by the wireless communicator 1, the switch controller 4
outputs channel usage information indicating the newly selected frequency
channel to the wireless communicator 1. When the switch controller 4 does
not change the frequency channel currently used by the wireless
communicator 1, the switch controller 4 outputs channel usage information
indicating the same channel as the currently used frequency channel to
the wireless communicator 1 (step ST8).

[0051] Thereafter, the wireless communicator 1 performs wireless
communication with another wireless communication device, using the
frequency channel indicated by the channel usage information output from
the switch controller 4.

[0052] As is clear from the above explanation, according to Embodiment 1,
the configuration is such that there are provided the wireless
communicator 1 that performs wireless communication with another wireless
communication device by using a frequency channel and, on the other hand,
performs channel scanning in a period during which the wireless
communication is not performed to detect frequency channels currently
used by surrounding wireless communication devices; the frequency channel
information storage 2 that stores frequency channel information
indicating the frequency channels detected by the wireless communicator
1; and the travel information acquisition unit 3 that acquires travel
information indicating the motion of a vehicle in which the wireless
communication device is installed, and the switch controller 4 performs
switching control of the frequency channel used by the wireless
communicator 1 in accordance with the frequency channel information
stored in the frequency channel information storage 2 and the travel
information acquired by the travel information acquisition unit 3.
Therefore, there is an effect of being able to suppress excessive channel
switching without causing an increase in the influence of interference on
the communication.

[0053] Specifically, the switch controller 4 is configured not to perform
switching control of the frequency channel used by the wireless
communicator 1 when a vehicle travel speed V acquired by the travel
information acquisition unit 3 is equal to or more than a predetermined
speed threshold Vth, and to perform switching control of the
frequency channel used by the wireless communicator 1 only when the
travel speed V is less than the speed threshold Vth. Since the
frequency channel switching is not performed under the state where the
period of time during which the communication is influenced by
interference is short (i.e. when the vehicle travels at high speed), the
excessive channel switching can be suppressed.

Embodiment 2

[0054]FIG. 3 is a configuration diagram showing a wireless communication
device according to Embodiment 2 of the present invention. In the
drawing, the same reference numerals as those in FIG. 1 indicate the same
or corresponding portions, and thus description thereof are omitted.

[0055] A frequency channel information storage 5 is composed of, for
example, a storage device such as a RAM or a hard disk, and stores
frequency channel information output from a wireless communicator 1.

[0056] On storing the frequency channel information output from the
wireless communicator 1, the frequency channel information storage 5
records the number C of detection of the frequency channels performed by
the wireless communicator 1.

[0057] The switch controller 4 is composed of, for example, a
semiconductor integrated circuit on which a CPU is mounted, a one-chip
microcomputer, or the like. The switch controller 4 performs switching
control of the frequency channel used by the wireless communicator 1 in
accordance with the frequency channel information stored in the frequency
channel information storage 5 and the travel information acquired by the
travel information acquisition unit 3.

[0058] Specifically, on changing the frequency channel used by the
wireless communicator 1, the switch controller 6 sets a higher
interference detection threshold Cth for a higher vehicle travel
speed V acquired by the travel information acquisition unit 3. The switch
controller 6 excludes, from selection, a frequency channel whose number C
of detection recorded in the frequency channel information storage 5
exceeds the interference detection threshold Cth, and selects a
frequency channel to be used by the wireless communicator 1 from among
usable frequency channels other than the excluded frequency channels.

[0059] In the example represented by FIG. 3, it is assumed that the
wireless communicator 1, the frequency channel information storage 5, the
travel information acquisition unit 3, and the switch controller 6, which
are the components of the wireless communication device is composed of
dedicated hardware. Alternatively, a part of those components or the
whole ones may be composed of a computer.

[0060] When the entire wireless communication device is composed of a
computer, a program in which the processing content of the wireless
communicator 1, the frequency channel information storage 5, the travel
information acquisition unit 3, and the switch controller 6 is written
may be stored in a memory of the computer, and thus a CPU of the computer
may implement the stored program in the memory.

[0061] In addition, when a part of the wireless communication device
(e.g., the switch controller 6) is composed of a computer, a program in
which the process content of the switch controller 6 is written may be
stored in a memory of the computer, and a CPU of the computer may
implement the stored program in the memory.

[0062]FIG. 4 is a flowchart showing the processing content of the switch
controller 6 of the wireless communication device according to Embodiment
2 of the present invention.

[0063] The operation will be described.

[0064] The wireless communicator 1 performs wireless communication with
another wireless communication device by using a frequency channel given
by the switch controller 6 which will be described later.

[0065] In addition, the wireless communicator 1 performs channel scanning
in a period during which the wireless communication is not performed in
order to detect frequency channels currently used by surrounding wireless
communication devices.

[0066] On detecting a frequency channel currently used by a surrounding
wireless communication device, the wireless communicator 1 measures a
received signal strength S of the detected frequency channel. The
wireless communicator 1 outputs frequency channel information including
information on the frequency channel and the received signal strengths S
to the frequency channel information storage 5.

[0068] On storing the frequency channel information output from the
wireless communicator 1, the frequency channel information storage 5
records the number C of detection of the frequency channels performed by
the wireless communicator 1.

[0069] When, for example, frequency channel CH1 and frequency channel CH2
are detected as frequency channels currently used by surrounding wireless
communication devices, each of the recorded number C of detection of the
frequency channels CH1 and CH2 is incremented.

[0070] Note that a value "0" is recorded as the number C of detection of a
frequency channel that has not been detected even once by the wireless
communicator 1 among one or more usable frequency channels.

[0071] The travel information acquisition unit 3 acquires, for example, a
vehicle travel speed V as travel information indicating motion of the
vehicle from a speedometer of the vehicle in which the wireless
communication device is installed.

[0073] After acquiring the frequency channel information, the switch
controller 6 recognizes the frequency channels currently used by the
surrounding wireless communication devices by referring to the frequency
channel information, and determines whether the frequency channels
include the same channel as or an adjacent channel to the frequency
channel currently used by the wireless communicator 1 (step ST12).

[0074] If the frequency channels currently used by the surrounding
wireless communication devices do not include the same or adjacent
channel as/to the frequency channel currently used by the wireless
communicator 1, the switch controller 6 does not change the frequency
channel currently used by the wireless communicator 1 because the
communication is not influenced by interference (step ST13).

[0075] On the other hand, if the frequency channels currently used by the
surrounding wireless communication devices include the same or adjacent
channel as/to the frequency channel currently used by the wireless
communicator 1, the switch controller 6 recognizes the received signal
strengths S of the frequency channels currently used by the surrounding
wireless communication devices by referring to the frequency channel
information because the communication may be influenced by interference.
Then the switch controller 6 determines whether the received signal
strengths S of the frequency channels are equal to or more than a
predetermined strength threshold Sth (step ST14).

[0076] If the received signal strengths S of the frequency channels
currently used by the surrounding wireless communication devices are less
than the strength threshold Sth, the switch controller 6 does not
change the frequency channel currently used by the wireless communicator
1 (step ST13). This is because it is less likely that the communication
is influenced by interference (even if the communication is influenced by
interference, the influence is considered to be small).

[0077] On the other hand, if the received signal strengths S of the
frequency channels currently used by the surrounding wireless
communication devices are equal to or more than the strength threshold
Sth, the switch controller 6 acquires the vehicle travel speed V
from the travel information acquisition unit 3 (step ST15). This is
because it is highly likely that the communication is influenced by
interference.

[0079] As the vehicle travel speed V is higher, the vehicle can speedily
go through a location where wireless communication is interfered, and
thereby comes off with a shorter time period of interference. For this
reason, a higher interference detection threshold Cth is set for a
higher travel speed V.

[0080] After setting the interference detection threshold Cth, the
switch controller 6 compares the number C of detection of each frequency
channel (one or more usable frequency channels) recorded in the frequency
channel information storage 5 with the interference detection threshold
Cth (step ST17). The switch controller 6 determines that the
frequency channel whose number C is more than the interference detection
threshold Cth is a frequency channel that are highly likely to
interfere the communication, and sets this frequency channel as a
unusable channel (step ST18).

[0081] On the other hand, the frequency channel whose number C is less
than the interference detection threshold Cth is set as a usable
channel (step ST19).

[0082] The switch controller 6 selects any one frequency channel from
among the frequency channels set as the usable channels (i.e. frequency
channels which are not set as the unusable channels) (step ST20).

[0083] When the switch controller 6 changes the frequency channel
currently used by the wireless communicator 1 (i.e. when the frequency
channels currently used by the surrounding wireless communication devices
include the same or adjacent channel as/to the frequency channel
currently used by the wireless communicator 1 and the received signal
strengths S of the frequency channels currently used by the surrounding
wireless communication devices are equal to or more than the strength
threshold Sth), the switch controller 6 outputs channel usage
information indicating the newly selected frequency channel to the
wireless communicator 1. When the switch controller 6 does not change the
frequency channel currently used by the wireless communicator 1, the
switch controller 6 outputs channel usage information indicating the same
channel as the currently used frequency channel to the wireless
communicator 1 (step ST21).

[0084] Thereafter, the wireless communicator 1 performs wireless
communication with another wireless communication device, using the
frequency channel indicated by the channel usage information output from
the switch controller 6.

[0085] As is clear from the above explanation, according to Embodiment 2,
the configuration is such that when the frequency channel used by the
wireless communicator 1 is changed, the switch controller 6 sets a higher
interference detection threshold Cth for a higher vehicle travel
speed V acquired by the travel information acquisition unit 3, excludes
from the selection the frequency channel whose number C of detection
recorded in the frequency channel information storage 5 exceeds the
interference detection threshold Cth, and selects a frequency
channel to be used by the wireless communicator 1 from among the usable
frequency channels other than the excluded frequency channels. Therefore,
under the circumstances where the period of time during which
communication is influenced by interference is short (i.e. where the
vehicle travel speed is high), the frequency channel switching is not
performed frequently, and thereby the advantage of being able to suppress
excessive channel switching is achieved.

[0086] Embodiment 2 presents that a higher interference detection
threshold Cth is set for a higher vehicle travel speed V acquired by
the travel information acquisition unit 3. Alternatively, a higher
strength threshold Sth can be set for the higher vehicle travel
speed V acquired by the travel information acquisition unit 3.

[0087] In the case where the higher strength threshold Sth is set for
a higher vehicle travel speed V, and the vehicle travel speed V is high,
a situation where the received signal strengths S of frequency channels
currently used by surrounding wireless communication devices are equal to
or more than the strength threshold Sth decreases. As a result, the
frequency channel switching is not performed frequently, and the
advantage of being able to suppress excessive channel switching is
achieved.

Embodiment 3

[0088] In the above-described Embodiment 1 presents that channel scanning
is performed in a period during which wireless communication is not
performed. Alternatively, the channel scanning may be performed when
surrounding condition of the vehicle has changed.

[0089]FIG. 5 is a configuration diagram showing a wireless communication
device according to Embodiment 3 of the present invention. In the
drawing, the same reference numerals as those in FIG. 1 indicate the same
or corresponding portions, and thus description thereof are omitted.

[0090] A wireless communicator 7 is composed of, for example, a
communication device in which a modulator, a demodulator, etc. are
mounted. The wireless communicator 7 performs the process of performing
wireless communication with another wireless communication device by
using a frequency channel given by a switch controller 9. The wireless
communicator 7 performs channel scanning when receiving a channel
detection request from the switch controller 9. The channel scanning is
performed to detect frequency channels currently used by surrounding
wireless communication devices.

[0091] A travel information acquisition unit 8 is composed of, for
example, a semiconductor integrated circuit on which a CPU is mounted, a
one-chip microcomputer, or the like. The travel information acquisition
unit 3 performs the process of acquiring a vehicle travel speed, a
vehicle travel location, vehicle acceleration/deceleration information,
and steering wheel operation information etc., as travel information
indicating the motion of the vehicle in which the wireless communication
device is installed.

[0092] The switch controller 9 is composed of, for example, a
semiconductor integrated circuit on which a CPU is mounted, a one-chip
microcomputer, or the like. The switch controller 9 determines whether
surrounding condition of the vehicle has changed by using the travel
information acquired by the travel information acquisition unit 8. When
the switch controller 9 determines that the surrounding condition has
changed, the switch controller 9 outputs a channel detection request to
the wireless communicator 7. The switch controller 9 performs switching
control of the frequency channel used by the wireless communicator 7 by
using frequency channel information stored in the frequency channel
information storage 2.

[0093] In the example represented by FIG. 5, it is assumed that the
wireless communicator 7, the frequency channel information storage 2, the
travel information acquisition unit 8, and the switch controller 9, which
are the components of the wireless communication device is composed of
dedicated hardware. Alternatively, a part of those components or the
whole ones may be composed of a computer.

[0094] When the entire wireless communication device is composed of a
computer, a program in which the processing content of the wireless
communicator 7, the frequency channel information storage 2, the travel
information acquisition unit 8, and the switch controller 9 is written
may be stored in a memory of the computer, and thus a CPU of the computer
may implement the stored program in the memory.

[0095] In addition, when a part of the wireless communication device
(e.g., the switch controller 9) is composed of a computer, a program in
which the process content of the switch controller 9 is written may be
stored in a memory of the computer, and a CPU of the computer may
implement the stored program in the memory.

[0096]FIG. 6 is a flowchart showing the processing content of the switch
controller 9 of the wireless communication device according to Embodiment
3 of the present invention.

[0097] The operation will be described.

[0098] The wireless communicator 7 performs wireless communication with
another wireless communication device by using a frequency channel given
by the switch controller 9 which will be described later.

[0099] When the wireless communicator 7 receives a channel detection
request from the switch controller 9, the wireless communicator 7
performs channel scanning in order to detect frequency channels currently
used by surrounding wireless communication devices.

[0100] On detecting a frequency channel currently used by a surrounding
wireless communication device, the wireless communicator 7 measures a
received signal strength S of the detected frequency channel. The
wireless communicator 7 outputs frequency channel information including
information on the frequency channel and the received signal strengths S
to the frequency channel information storage 2.

[0102] The travel information acquisition unit 8 acquires, for example, a
vehicle travel speed V as travel information indicating motion of the
vehicle from a speedometer of the vehicle in which the wireless
communication device is installed.

[0103] The travel information acquisition unit 8 further acquires a
vehicle travel location from a navigation device, in which the wireless
communication device is installed, as travel information indicating the
motion of the vehicle.

[0107] When the vehicle is traveling on a straight road, the communication
conditions do not change greatly because the relation with other vehicles
traveling around the user's vehicle does not change greatly. However,
after the user's vehicle passes an intersection or a fork, the
communication conditions may change greatly. This is because there may be
a situation where surrounding vehicles traveling in the same direction to
the user's vehicle are no longer present or a situation where a vehicle
which has not been present around the user's vehicle appears.

[0108] Hence, the switch controller 9 compares the vehicle travel location
with the map information and determines that the vehicle's surrounding
condition has changed when, for instance, the vehicle passes an
intersection or a fork.

[0109] Although it is shown here that the switch controller 9 determines
whether the vehicle's surrounding condition has changed by comparing the
vehicle travel location with the map information, the switch controller 9
may determine that the vehicle surrounding condition has changed when a
travel speed V which is vehicle travel information has changed or when
acceleration or deceleration above a certain level is performed or when
steering wheel operation has changed (e.g., steering wheel operation
associated with lane change), or the like.

[0110] When a determination is made such that the vehicle's surrounding
condition has not changed, the switch controller 9 does not change the
frequency channel currently used by the wireless communicator 7 (step
ST33). This is because it is highly likely that the communication
conditions have not changed greatly.

[0111] On the other hand, when a determination is made such that the
vehicle's surrounding condition has changed, the switch controller 9
outputs a channel detection request to the wireless communicator 7
because it is highly likely that the communication conditions have
changed greatly (step ST34).

[0112] If the wireless communicator 7 is not performing wireless
communication with another wireless communication device, the wireless
communicator 7 performs channel scanning in response to the channel
detection request output from the switch controller 9 to detect frequency
channels currently used by surrounding wireless communication devices.

[0115] After acquiring the frequency channel information, the switch
controller 9 recognizes the frequency channels currently used by the
surrounding wireless communication devices by referring to the frequency
channel information, and determines whether the frequency channels
include the same channel as or an adjacent channel to the frequency
channel currently used by the wireless communicator 7 (step ST36).

[0116] If the frequency channels currently used by the surrounding
wireless communication devices do not include the same or adjacent
channel as/to the frequency channel currently used by the wireless
communicator 7, the switch controller 9 does not change the frequency
channel currently used by the wireless communicator 7 because the
communication is not influenced by interference (step ST33).

[0117] On the other hand, if the frequency channels currently used by the
surrounding wireless communication devices include the same or adjacent
channel as/to the frequency channel currently used by the wireless
communicator 7, the switch controller 9 recognizes the received signal
strengths S of the frequency channels currently used by the surrounding
wireless communication devices by referring to the frequency channel
information because the communication may be influenced by interference.
Then the switch controller 9 determines whether the received signal
strengths S of the frequency channels are equal to or more than a
predetermined strength threshold Sth (step ST37).

[0118] If the received signal strengths S of the frequency channels
currently used by the surrounding wireless communication devices are less
than the strength threshold Sth, the switch controller 9 does not
change the frequency channel currently used by the wireless communicator
7 (step ST33). This is because it is less likely that the communication
is influenced by interference (even if the communication is influenced by
interference, the influence is considered to be small).

[0119] On the other hand, if the received signal strengths S of the
frequency channels currently used by the surrounding wireless
communication devices are equal to or more than the strength threshold
Sth, the switch controller 9 changes the frequency channel currently
used by the wireless communicator 7 because it is highly likely that the
communication is influenced by interference.

[0120] Specifically, the switch controller 9 selects any one frequency
channel from among usable frequency channels other than the frequency
channels included in the frequency channel information stored in the
frequency channel information storage 2 (step ST38).

[0121] When the switch controller 9 changes the frequency channel
currently used by the wireless communicator 7 (i.e. when the frequency
channels currently used by the surrounding wireless communication devices
include the same or adjacent channel as/to the frequency channel
currently used by the wireless communicator 7 and the received signal
strengths S of the frequency channels currently used by the surrounding
wireless communication devices are equal to or more than the strength
threshold Sth), the switch controller 9 outputs channel usage
information indicating the newly selected frequency channel to the
wireless communicator 7. When the switch controller 9 does not change the
frequency channel currently used by the wireless communicator 7, the
switch controller 9 outputs channel usage information indicating the same
channel as the currently used frequency channel to the wireless
communicator 7 (step ST39).

[0122] Thereafter, the wireless communicator 7 performs wireless
communication with another wireless communication device, using the
frequency channel indicated by the channel usage information output from
the switch controller 9.

[0123] As is clear from the above, according to Embodiment 3, the
configuration is such that the switch controller 9 determines whether the
vehicle's surrounding condition has changed based on travel information
acquired by the travel information acquisition unit 8. If the switch
controller 9 determines that the surrounding condition has changed, the
switch controller 9 outputs a channel detection request to the wireless
communicator 7. On the other hand, the switch controller 9 performs
switching control of a frequency channel used by the wireless
communicator 7 in accordance with frequency channel information stored in
the frequency channel information storage 2. Therefore, under the
circumstances where the communication conditions have not changed greatly
(i.e. where the vehicle's surrounding condition has not changed), the
frequency channel switching is not performed, and thereby the advantage
of being able to suppress excessive channel switching is achieved.

[0124] Embodiment 3 presents that the frequency channel currently used by
the wireless communicator 7 is changed when frequency channels currently
used by surrounding wireless communication devices include the same or
adjacent channel as/to the frequency channel currently used by the
wireless communicator 7 and the received signal strengths S of the
frequency channels currently used by the surrounding wireless
communication devices are equal to or more than the strength threshold
Sth. Alternatively, as in the above-described Embodiment 1, the
frequency channel currently used by the wireless communicator 7 may be
changed on a condition that a vehicle travel speed V is less than a speed
threshold Vth.

Embodiment 4

[0125] In the above-described Embodiment 1 presents that a wireless
communicator 1 performs channel scanning in a period during which
wireless communication is not performed, and detects frequency channels
currently used by surrounding wireless communication devices.
Alternatively, only a specified frequency channel may be detected instead
of all of the frequency channels currently used by the surrounding
wireless communication devices.

[0126] FIG. 7 is a configuration diagram showing a wireless communication
device according to Embodiment 4 of the present invention. In the
drawing, the same reference numerals as those in FIG. 1 indicate the same
or corresponding portions and thus description thereof are omitted.

[0127] A wireless communicator 10 is composed of, for example, a
communication device in which a modulator, a demodulator, etc. are
mounted. The wireless communicator 10 performs the process of performing
wireless communication with another wireless communication device by
using a frequency channel given by a switch controller 11. The wireless
communicator 10 performs channel scanning in a period during which the
wireless communication is not performed. The channel scanning is
performed to detect frequency channels included in a channel detection
list output from the switch controller 11.

[0128] The switch controller 11 is composed of, for example, a
semiconductor integrated circuit on which a CPU is mounted, a one-chip
microcomputer, or the like. The switch controller 11 outputs to the
wireless communicator 10 a channel detection list including the channel
numbers of frequency channels as detection targets in accordance with
travel information acquired by a travel information acquisition unit 3.
The switch controller 11 performs switching control of the frequency
channel used by the wireless communicator 10 by using frequency channel
information stored in a frequency channel information storage 2.

[0129] The switch controller 11 is configured to set a smaller number of
channel numbers included in a channel detection list for a higher vehicle
travel speed V acquired by the travel information acquisition unit 3.

[0130] In the example represented by FIG. 7, it is assumed that the
wireless communicator 10, the frequency channel information storage 2,
the travel information acquisition unit 3, and the switch controller 11,
which are the components of the wireless communication device is composed
of dedicated hardware. Alternatively, a part of those components or the
whole ones may be composed of a computer.

[0131] When the entire wireless communication device is composed of a
computer, a program in which the processing content of the wireless
communicator 10, the frequency channel information storage 2, the travel
information acquisition unit 3, and the switch controller 11 is written
may be stored in a memory of the computer, and thus a CPU of the computer
may implement the stored program in the memory.

[0132] In addition, when a part of the wireless communication device
(e.g., the switch controller 11) is composed of a computer, a program in
which the process content of the switch controller 11 is written may be
stored in a memory of the computer, and a CPU of the computer may
implement the stored program in the memory.

[0133]FIG. 8 is a flowchart showing the processing content of the switch
controller 11 of the wireless communication device according to
Embodiment 4 of the present invention.

[0134] The operation will be described.

[0135] The wireless communicator 10 performs wireless communication with
another wireless communication device by using a frequency channel given
by the switch controller 11 which will be described later.

[0136] In addition, the wireless communicator 10 performs channel scanning
in a period during which the wireless communication is not performed in
order to detect frequency channels currently used by surrounding wireless
communication devices.

[0137] Note that the wireless communicator 10 detects only frequency
channels with channel numbers included in a channel detection list output
from the switch controller 11, which will be described later, instead of
all frequency channels currently used by surrounding wireless
communication devices.

[0138] On detecting a frequency channel currently used by a surrounding
wireless communication device, the wireless communicator 10 measures a
received signal strength S of the detected frequency channel. The
wireless communicator 10 outputs frequency channel information including
information on the frequency channel and the received signal strengths S
to the frequency channel information storage 2.

[0140] The travel information acquisition unit 3 acquires, for example, a
vehicle travel speed V as travel information indicating motion of the
vehicle from a speedometer of the vehicle in which the wireless
communication device is installed.

[0142] After acquiring the vehicle travel speed V, the switch controller
11 creates, according to the travel speed V, a channel detection list
including the channel numbers of frequency channels as detection targets,
and outputs the channel detection list to the wireless communicator 10
(step ST42).

[0143] If the vehicle travel speed V is high, the time required for the
vehicle to get away from a location where the communication is interfered
is short, and thus the period of time during which the communication is
influenced by the interference is short. In this situation, the necessity
to change the frequency channel is low. Hence, the switch controller 11
sets a smaller number of channel numbers, included in the channel
detection list, for a higher vehicle travel speed V.

[0144] When the wireless communicator 10 is not performing wireless
communication with other wireless communication devices, the wireless
communicator 10 detects frequency channels with channel numbers included
in the channel detection list output from the switch controller 11.

[0147] After acquiring the frequency channel information, the switch
controller 11 recognizes the frequency channels currently used by the
surrounding wireless communication devices by referring to the frequency
channel information, and determines whether the frequency channels
include the same channel as or an adjacent channel to the frequency
channel currently used by the wireless communicator 10 (step ST44).

[0148] If the frequency channels currently used by the surrounding
wireless communication devices do not include the same or adjacent
channel as/to the frequency channel currently used by the wireless
communicator 10, the switch controller 11 does not change the frequency
channel currently used by the wireless communicator 10 because the
communication is not influenced by interference (step ST45).

[0149] On the other hand, if the frequency channels currently used by the
surrounding wireless communication devices include the same or adjacent
channel as/to the frequency channel currently used by the wireless
communicator 10, the switch controller 11 recognizes the received signal
strengths S of the frequency channels currently used by the surrounding
wireless communication devices by referring to the frequency channel
information because the communication may be influenced by interference.
Then the switch controller 11 determines whether the received signal
strengths S of the frequency channels are equal to or more than a
predetermined strength threshold Sth (step ST46).

[0150] If the received signal strengths S of the frequency channels
currently used by the surrounding wireless communication devices are less
than the strength threshold Sth, the switch controller 11 does not
change the frequency channel currently used by the wireless communicator
10 (step ST45). This is because it is less likely that the communication
is influenced by interference (even if the communication is influenced by
interference, the influence is considered to be small).

[0151] On the other hand, if the received signal strengths S of the
frequency channels currently used by the surrounding wireless
communication devices are equal to or more than the strength threshold
Sth, the switch controller 11 changes the frequency channel
currently used by the wireless communicator 10 because it is highly
likely that the communication is influenced by interference.

[0152] Specifically, the switch controller 11 selects any one frequency
channel from among usable frequency channels other than the frequency
channels included in the frequency channel information stored in the
frequency channel information storage 2 (step ST47).

[0153] When the switch controller 11 changes the frequency channel
currently used by the wireless communicator 10 (i.e. when the frequency
channels currently used by the surrounding wireless communication devices
include the same or adjacent channel as/to the frequency channel
currently used by the wireless communicator 10 and the received signal
strengths S of the frequency channels currently used by the surrounding
wireless communication devices are equal to or more than the strength
threshold Sth), the switch controller 11 outputs channel usage
information indicating the newly selected frequency channel to the
wireless communicator 10. When the switch controller 11 does not change
the frequency channel currently used by the wireless communicator 10, the
switch controller 11 outputs channel usage information indicating the
same channel as the currently used frequency channel to the wireless
communicator 10 (step ST48).

[0154] Thereafter, the wireless communicator 10 performs wireless
communication with another wireless communication device, using the
frequency channel indicated by the channel usage information output from
the switch controller 11.

[0155] As is clear from the above, according to Embodiment 4, the
configuration is such that the switch controller 11 sets a smaller number
of channel numbers, included in a channel detection list, for a higher
vehicle travel speed V acquired by the travel information acquisition
unit 3. Thus, under the circumstances where the necessity to change a
frequency channel is low (i.e. where the vehicle travel speed is high),
the time required to detect frequency channels is reduced, and thereby
the advantage of being able to reduce the time required to switch the
frequency channel is achieved. In addition, by the reduction in the time
required to detect frequency channels, even under the circumstances where
wireless communication is frequently performed, there is an advantage of
being able to detect frequency channels during a short period during
which wireless communication is not performed.

[0156] Furthermore, since frequency channel switching is not performed
frequently, the advantage of being able to suppress excessive channel
switching is achieved.

[0157] Embodiment 4 presents that the frequency channel currently used by
the wireless communicator 10 is changed when frequency channels currently
used by surrounding wireless communication devices include the same or
adjacent channel as/to the frequency channel currently used by the
wireless communicator 10 and the received signal strengths S of the
frequency channels currently used by the surrounding wireless
communication devices are equal to or more than the strength threshold
Sth. Alternatively, as in the above-described Embodiment 1, the
frequency channel currently used by the wireless communicator 10 may be
changed on a condition that a vehicle travel speed V is less than a speed
threshold Vth.

Embodiment 5

[0158]FIG. 9 is a configuration diagram showing a wireless communication
device according to Embodiment 5 of the present invention. In the
drawing, the same reference numerals as those in FIG. 1 indicate the same
or corresponding portions and thus description thereof are omitted.

[0159] A switching time information storage 12 is composed of, for
example, a storage device such as a RAM or a hard disk, and stores
switching time information indicating a frequency channel used after
switching control by a switch controller 13 and a switching time at which
the switching control is performed.

[0160] The switch controller 13 is composed of, for example, a
semiconductor integrated circuit on which a CPU is mounted, a one-chip
microcomputer, or the like. The switch controller 13 performs switching
control of the frequency channel used by the wireless communicator 1 in
accordance with the frequency channel information stored in the frequency
channel information storage 2, the travel information acquired by the
travel information acquisition unit 3, and the switching time information
stored in the switching time information storage 12.

[0161] Specifically, when a vehicle travel speed V acquired by the travel
information acquisition unit 3 is equal to or more than a predetermined
speed threshold Vth, the switch controller 13 does not perform the
switching control of the frequency channel used by the wireless
communicator 1.

[0162] On the other hand, if the travel speed V is less than the speed
threshold Vth, the switch controller 13 calculates, by referring to
the switching time information stored in the switching time information
storage 12, elapsed time T from when the frequency channel is last
switched. If the elapsed time T is less than an elapsed time threshold
Tth, the switch controller 13 does not perform switching control of
the frequency channel used by the wireless communicator 1. If the elapsed
time T is equal to or more than the elapsed time threshold Tth, the
switch controller 13 performs switching control of the frequency channel
used by the wireless communicator 1.

[0163] In the example represented by FIG. 9, it is assumed that the
wireless communicator 1, the frequency channel information storage 2, the
travel information acquisition unit 3, the switching time information
storage 12, and the switch controller 13, which are the components of the
wireless communication device is composed of dedicated hardware.
Alternatively, a part of those components or the whole ones may be
composed of a computer.

[0164] When the entire wireless communication device is composed of a
computer, a program in which the processing content of the wireless
communicator 1, the frequency channel information storage 2, the
switching time information storage 12, the travel information acquisition
unit 13, and the switch controller 13 is written may be stored in a
memory of the computer, and thus a CPU of the computer may implement the
stored program in the memory.

[0165] In addition, when a part of the wireless communication device
(e.g., the switch controller 13) is composed of a computer, a program in
which the process content of the switch controller 13 is written may be
stored in a memory of the computer, and a CPU of the computer may
implement the stored program in the memory.

[0166] FIG. 10 is a flowchart showing the processing content of the switch
controller 13 of the wireless communication device according to
Embodiment 5 of the present invention.

[0167] The operation will be described.

[0168] The wireless communicator 1 performs wireless communication with
another wireless communication device by using a frequency channel given
by the switch controller 13 which will be described later.

[0169] In addition, the wireless communicator 1 performs channel scanning
in a period during which the wireless communication is not performed in
order to detect frequency channels currently used by surrounding wireless
communication devices.

[0170] On detecting a frequency channel currently used by a surrounding
wireless communication device, the wireless communicator 1 measures a
received signal strength S of the detected frequency channel. The
wireless communicator 1 outputs frequency channel information including
information on the frequency channel and the received signal strengths S
to the frequency channel information storage 2.

[0172] The switching time information storage 12 stores switching time
information indicating a frequency channel used after switching control
by the switch controller 13 and a switching time at which the switching
control is performed.

[0173] Specifically, when the switch controller 13 performs frequency
channel switching control and thereby switches a frequency channel
indicated by the last switching time information stored to another
frequency channel, the switching time information storage 12 stores
switching time information indicating the frequency channel used after
the switching control and a switching time at which the switching control
is performed.

[0174] The travel information acquisition unit 3 acquires, for example, a
vehicle travel speed V as travel information indicating motion of the
vehicle from a speedometer of the vehicle in which the wireless
communication device is installed.

[0176] After acquiring the frequency channel information, the switch
controller 13 recognizes the frequency channels currently used by the
surrounding wireless communication devices by referring to the frequency
channel information, and determines whether the frequency channels
include the same channel as or an adjacent channel to the frequency
channel currently used by the wireless communicator 1 (step ST51).

[0177] If the frequency channels currently used by the surrounding
wireless communication devices do not include the same or adjacent
channel as/to the frequency channel currently used by the wireless
communicator 1, the switch controller 13 does not change the frequency
channel currently used by the wireless communicator 1 because the
communication is not influenced by interference (step ST52).

[0178] On the other hand, if the frequency channels currently used by the
surrounding wireless communication devices include the same or adjacent
channel as/to the frequency channel currently used by the wireless
communicator 1, the switch controller 13 recognizes the received signal
strengths S of the frequency channels currently used by the surrounding
wireless communication devices by referring to the frequency channel
information because the communication may be influenced by interference.
Then the switch controller 13 determines whether the received signal
strengths S of the frequency channels are equal to or more than a
predetermined strength threshold Sth (step ST53).

[0179] If the received signal strengths S of the frequency channels
currently used by the surrounding wireless communication devices are less
than the strength threshold Sth, the switch controller 13 does not
change the frequency channel currently used by the wireless communicator
1 (step ST52). This is because it is less likely that the communication
is influenced by interference (even if the communication is influenced by
interference, the influence is considered to be small).

[0180] On the other hand, if the received signal strengths S of the
frequency channels currently used by the surrounding wireless
communication devices are equal to or more than the strength threshold
Sth, the switch controller 13 acquires the vehicle travel speed V
from the travel information acquisition unit 3 (step ST54). This is
because it is highly likely that the communication is influenced by
interference.

[0181] After acquiring the vehicle travel speed V from the travel
information acquisition unit 3, the switch controller 13 determines
whether the vehicle travel speed V is equal to or more than a
predetermined speed threshold Vth, (step ST55).

[0182] If the vehicle travel speed V is equal to or more than the
predetermined speed threshold Vth, the switch controller 13 does not
change the frequency channel currently used by the wireless communicator
1 (step ST52). This is because it is considered that the time required
for the vehicle to get away from a location where the communication is
interfered is short, and thus the period of time during which the
communication is influenced by the interference is short.

[0183] If the vehicle travel speed V is less than the predetermined speed
threshold Vth, the switch controller 13 acquires the switching time
information from the switching time information storage 12 (step ST56),
and calculates elapsed time T from when the frequency channel is last
switched, by referring to the switching time information (step ST57).

[0184] After calculating the elapsed time T from when the frequency
channel is last switched, the switch controller 13 determines whether the
elapsed time T is equal to or more than a predetermined elapsed time
threshold Tth (step ST58).

[0185] If the elapsed time T from when the frequency channel is last
switched is less than the elapsed time threshold Tth, the switch
controller 13 does not change the frequency channel currently used by the
wireless communicator 1 (step ST52). This is because it is considered
that the temporary influence of interference by other vehicles traveling
at a higher speed than that of the vehicle, etc., is occurring. By this
control, frequent frequency channel switching can be avoided.

[0186] On the other hand, if the elapsed time T is equal to or more than
the elapsed time threshold Tth, the switch controller 13 changes the
frequency channel currently used by the wireless communicator 1. This is
because it is considered that a communication environment by the
influence of interference from a fixed access point, etc., has changed
with the motion of the vehicle.

[0187] Specifically, the switch controller 13 selects any one frequency
channel from among usable frequency channels other than the frequency
channels included in the frequency channel information stored in the
frequency channel information storage 2 (step ST59).

[0188] When the switch controller 13 changes the frequency channel
currently used by the wireless communicator 1 (i.e. when the frequency
channels currently used by the surrounding wireless communication devices
include the same or adjacent channel as/to the frequency channel
currently used by the wireless communication device 1, the received
signal strengths of the frequency channels currently used by the
surrounding wireless communication devices are equal to or more than the
strength threshold Sth, the vehicle travel speed is less than the
speed threshold value Vth, and the elapsed time T from the last
switching time is equal to or more than the elapsed time threshold
Tth), the switch controller 13 outputs channel usage information
indicating the newly selected frequency channel to the wireless
communicator 1.

[0189] When the switch controller 13 does not change the frequency channel
currently used by the wireless communicator 1, the switch controller 6
outputs channel usage information indicating the same channel as the
currently used frequency channel to the wireless communicator 1 (step
ST60).

[0190] Thereafter, the wireless communicator 1 performs wireless
communication with another wireless communication device, using the
frequency channel indicated by the channel usage information output from
the switch controller 13.

[0191] As is clear from the above, according to Embodiment 5, the
configuration is such that even when the vehicle speed V of the vehicle
is less than or equal to the speed threshold Vth, if the elapsed
time T from the last frequency channel switching time is less than the
elapsed time threshold Tth, the frequency channel used by the
wireless communicator 1 is not switched. Thus, there is an advantage of
being able to prevent the occurrence of a situation where the frequency
channel is frequently switched due to the temporary influence of
interference by other vehicles traveling at a higher speed than that of
the vehicle, etc.

[0192] Note that the invention of the present application allows free
combinations of Embodiments, or modifications to any component in
Embodiments, or omission of any component in Embodiments within the scope
of the present invention.

INDUSTRIAL APPLICABILITY

[0193] The wireless communication device according to the invention is
suitable for use as a device that selects an arbitrary frequency channel
from among a plurality of frequency channels and performs wireless
communication with another wireless communication device installed in
another vehicle, using the frequency channel.

Patent applications by Kumiko Isu, Tokyo JP

Patent applications by Shu Murayama, Tokyo JP

Patent applications by Mitsubishi Electric Corporation

Patent applications in class TRANSMITTER AND RECEIVER AT SEPARATE STATIONS

Patent applications in all subclasses TRANSMITTER AND RECEIVER AT SEPARATE STATIONS